Routing method and device of mobile ad-hoc networks

ABSTRACT

A network construction method, a routing method and device of mobile ad-hoc networks are provided. The mobile ad-hoc network includes a plurality of nodes, each node communicating with its neighbors via communication links. The routing method comprises the following steps: each node identifying a link quality with each of its neighbors by providing marks based on a hysteresis-based link quality marking mechanism; each node identifying a link operationality with each of its neighbors by evaluating a score calculated from the marks; and each node reconstructing routes with its neighbors by filtering route construction messages related to the link operationality of the neighbors.

This application is a continuation of U.S. application Ser. No.16/777,388 filed on Jan. 30, 2020, the disclosure of which isincorporated herein by reference.

FIELD

This invention relates to the field of wireless communication networks,and more specifically to Mobile Ad-hoc NETworks (MANETs), and relatedrouting methods and devices.

BACKGROUND

Traditionally, wireless networks operate in one of two topologies:infrastructure or ad-hoc mode. In the infrastructure topology, allcommunications among wireless nodes must go through a centralPoint-of-Attachment (PoA) which typically has higher processing andtransmission capabilities but is much more expensive than the rest ofthe wireless nodes in this topology. In the ad-hoc topology, wirelessnodes directly communicate with each other without the need for acentral PoA. While the setup of ad-hoc networks is simpler, faster, andcheaper than infrastructure-based networks, the handover management ismore complex.

In infrastructure-based networks, handing off a session between two PoAsis handled in three ways: (1) Network-Controlled Handoff: In anetwork-controlled handoff procedure, the network makes a handoffdecision based on the signal measurements of the mobile node at a numberof PoAs; (2) Mobile-Assisted Handoff: In a mobile-assisted handoffprocedure, the mobile node takes measurements and forwards thesemeasurements to the network which, in turn, makes the decision; and (3)Mobile-Controlled Handoff: In mobile-controlled handoff procedure, eachmobile node is completely in control of the handoff process.

In traditional ad-hoc networks, on the other hand, only themobile-controlled handoff is used due to the lack of centralizedmanagement.

Typically, a handoff is triggered when specific link-level measurementsmeet certain criteria. For example, the Received Signal StrengthIndicator (RSSI), Bit Error Rate (BER), and Packet Error Rate (PER) arelink-level measurements used to trigger a handoff. FIG. 1 depicts ahysteresis-based handoff criterion between two PoAs. In this examplehandoff scheme, the handoff is executed when the RSSI of the old PoA islower than a predefined threshold, H, and the RSSI of the new PoA ishigher than that of the old one by a predefined margin, h.

Due to the centralized management in infrastructure-based networks,changing the PoA is sufficient to reconstruct the packet route. The oldPoA and the new PoA communicate with each other to re-route packetsthrough the new PoA thereby avoiding the unidirectional link problem.The unidirectional link problem is when transmission is successful inone direction but not in the other. However, due to the distributedmanagement in ad-hoc networks, a link that becomes unidirectional causesa failure to reconstruct the broken routes.

Conventional ad-hoc networks do not describe specific requirements forthe deployment of the fixed portion of the network. Poorly constructednetworks will impact the performance of any hand-off algorithm. A poorlyconstructed network may include areas of coverage gaps or insufficientcoverage overlap. Most ad-hoc routing algorithms assume that thewireless links among the network nodes are bidirectional. However, thisassumption is not always true, whereby some links could beunidirectional due to differences in transmission power and receiversensitivity of the different nodes. Due to node mobility, bidirectionallinks may turn into unidirectional ones for a period of time beforedisconnection. The presence of unidirectional links severely affects theperformance of ad-hoc routing protocols and prevents the ability toreconstruct routes in a timely manner. Although some protocolsfacilitate transmitting packets over asymmetric routes to overcome theunidirectional link problem, these solutions require modifying the MediaAccess Control (MAC) layer, causing increased complexity and cost.

Some ad-hoc networks use link quality metric (e.g., RSSI, BER, SNR andSNIR) to determine whether the link to a given node can be part of aroute or not. This link quality metric ensures that the quality of thelinks is high and prevents unnecessary route changes. The list of nodeswith acceptable links is known as the neighbors list. Sendinginformation about the neighbors' list is called a neighboradvertisement. To proactively identify link directionality, andtherefore solve the unidirectional link problem, a neighboradvertisement technique can be used where each node periodicallybroadcasts a hello message containing its own neighbors' list. When twoadjacent nodes find their own address in each other's neighboradvertisement, they identify the link between them as bidirectional. Ifone node does not hear its own address in its neighbor's neighboradvertisement, it identifies that link as unidirectional. However,relying only on periodic neighbor advertisements to identify linkdirectionality significantly increases the time required to detectchanges in link-status, thereby increasing the route reconstructiontime.

Other methods have also been developed with the intent to solve theunidirectional link problem. For example, in table-driven routingprotocols, such as the Destination Sequenced Distance Vector (DSDV)routing protocol discussed in the book “Ad Hoc Networking” by Perkins,Charles E. Vol. 1. Published by Addison-Wesley in 2001, hereinexplicitly incorporated by reference in its entirety, linkdirectionality is identified by periodically exchanging the routingtables among the various nodes and asymmetric routes are constructed toovercome the unidirectional link problems. However, the exchange of therouting table substantially increases the network overhead and reducesthe network capacity. Besides affecting the scalability of the solution,exchanging routing tables to reconstruct failed routes significantlyincreases the route reconstruction time, thereby severely deterioratingthe Quality of Service (QoS) of ongoing sessions, especially sessionsrequiring stringent real-time communications such as VoIP or videocalls.

In on-demand routing protocols, such as the Dynamic Source Routing (DSR)discussed in “The dynamic source routing protocol (DSR) for mobile adhoc networks” by Johnson, David, Yin-chun Hu, and David Maltz, IPv4. No.RFC 4728. 2007, and discussed in “Ad hoc on-demand distance vector(AODV) routing” by Perkins, Charles, Elizabeth Belding-Royer, and SamirDas, No. RFC 3561. 2003, herein both explicitly incorporated byreference in their entireties, the directionality of links is identifiedat route construction time by using link-level acknowledgements of routeconstruction messages. The absence of these link-level acknowledgementsmeans that one node does not hear the other node (e.g., the link betweenthem is unidirectional).

In DSR, the recipient of a Route Reply (RREP) is required to acknowledgethis reception by sending back a RREP acknowledgement (RREP-Ack). Whenthe RREP sender does not receive a RREP-Ack, the RREP sender broadcaststhe RREP so as to construct an alternative reverse route. Relying onlink-level acknowledgement (Acks) for the route construction messagesincreases the network overhead and increases the route reconstructiontime, decreasing the network capacity, and degrading the supported QoS.In addition, forwarding unicast packets over unidirectional reverselinks requires making some changes to the MAC layer functionality suchthat the MAC layer accepts indirect Acks.

In AoDV, the recipient of a RREP is optionally required to send back aRREP-Ack. If the RREP sender node does not receive a RREP-Ack, the RREPsender puts that recipient node in a blacklist, ignoring any futureRoute Requests (RREQs) from the RREP recipient for a predefined time.Besides decreasing the network capacity, relying on link-levelacknowledgements for the route construction messages to detect changesin link status significantly increases the route reconstruction time anddeteriorates the supported QoS.

In “Fast and accurate link discovery integrated with reliable multicast”by Lertpratchya, Daniel, Douglas M. Blough, and George F. Riley, in802.11. Georgia Institute of Technology, published in 2013, hereinexplicitly incorporated by reference in its entirety, a reliablemulticasting technique for both neighbor discovery and unidirectionallink detection was proposed. Although the proposed technique efficientlyidentifies the link directionality and promptly detects any change inthe link status (e.g., directionality), the technique requires modifyingthe MAC layer functionality. In addition, the technique significantlyincreases the network overhead as all nodes are required to acknowledgethe reception of each multicast message thereby affecting thescalability of this solution.

SUMMARY

Therefore, the need to create a scalable well-constructed broadbandMobile Ad-hoc NETwork (MANET) that provides seamless mobility over alarge coverage area may be addressed herein.

The MANET may be constructed to avoids the pitfalls of a poorlyconstructed network.

The MANET may be able to reconstruct routes fast enough to meet thecriteria of demanding applications such as Voice over IP (VOIP) andreal-time video.

Any and all aspects as described herein, individually or in anycombination consistent within the understanding of one of skill in theart upon reviewing the disclosure herein.

According to an aspect, a routing method of a mobile ad-hoc network mayinclude a plurality of nodes, each node communicating with at least oneneighbor via at least one communication link. The method may comprise:each node transmitting an advertisement; each node identifying a linkquality with each of the at least one neighbor providing at least onemark based on a link quality metric; each node identifying a linkoperationality with each of the at least one neighbor by evaluating ascore calculated from the at least one mark; and each nodereconstructing at least one route with the at least one neighbor byfiltering at least one route construction message related to the linkoperationality of the at least one neighbor. The link quality metric maybe hysteresis-based.

The step of identifying the link quality may compare the link qualitymetric received from the advertisement of the at least one neighbor witha high threshold and a low threshold. The link quality metric maycomprise: marking the link quality as high when the link quality metricexceeds the high threshold; marking the link quality as low when thelink quality metric falls below the low threshold; marking the linkquality as high when the link quality metric falls below the highthreshold, and before the link quality metric falls below the lowthreshold; marking the link quality as low when the link quality metricrises above the low threshold, and before the link quality metricexceeds the high threshold; and marking the link quality as low if atimeout timer for receiving the advertisement expires before receiving anew advertisement from the at least one neighbor.

The link quality metric may be selected from at least one of: a receivedsignal strength indicator (RSSI), a Bit Error Rate (BER), a Signal toNoise Ratio (SNR), a Signal to Noise and Interference Ratio (SNIR), andany combination thereof.

The low threshold may be selected to be higher than a sensitivity of arecipient node.

The step of identifying link operationality may compare the score with ascore-operational (SOP) criterion and with a Score-Non-Operational(SNOP) criterion. The step of identifying link operationality mayidentify a link-from-neighbor operationality and a link-to-neighboroperationality. The step of identifying the link-from-neighboroperationality may comprise: marking the link-from-neighbor asdirectionally Operational (OP) when the score meets the SOP criterion;marking the link-from-neighbor as directionally Non-Operational (NOP)when the score meets the SNOP criterion; and keeping thelink-from-neighbor as a previous status when the score does not meet theSOP criterion and the SNOP criterion. The step of identifying thelink-to-neighbor operationality may comprise: marking thelink-to-neighbor as directionally NOP when each node does not find eachnode's own IP address in the advertisement; marking the link-to-neighboras Going-Non-Operational (GNOP) when the score to the at least oneneighbor meets the SNOP criterion when each node finds each node's ownIP address in the advertisement; and marking the link-to-neighbor asdirectionally OP when the score to the at least one neighbor does notmeet the SNOP criterion when each node finds each node's own IP addressin the advertisement. The step of identifying link operationality maydetermine the link-from-neighbor operationality and the link-to-neighboroperationality under data packet transmission failure.

The score to the at least one neighbor may be calculated based on thelink quality metric of an advertised last j marks.

A link-with-neighbor may be marked as bidirectionally OP when bothlink-from-neighbor and link-to-neighbor meet the OP criterion.

The routing method may comprise: broadcasting a Route Failure Message(RFM) when a link-with-neighbor is marked as NOP.

The step of determining the link-from-neighbor operationality and thelink-to-neighbor operationality under data packet transmission failuremay comprise: increasing a packet retransmission counter by 1 when adata packet transmission has failed; increasing a dropped packet counterby 1 when the data packet retransmission counter exceeds a predeterminednumber of retransmission tries, R; and marking both the link-to-neighborand the link-from-neighbor as NOP when the dropped packet counterexceeds a predetermined number of dropped packets, N.

The routing method may retransmit data packet when the data packetretransmission counter is below the predetermined number ofretransmission tries, R.

The routing method may reset the packet retransmission counter, andretransmitting data packet when the dropped packet counter is below thepredetermined number of dropped packets, N.

The step of filtering route construction messages may respond to a SeekRoute Message (SRM) from the at least one neighbor and responding to theRFM from the at least one neighbor.

The responding to SRM may comprise: discarding the received SRM wheneach node receives an SRM over a NOP link-with-neighbor; and discardingthe received SRM if the link-to-neighbor is marked as GNOP when eachnode receives an SRM over an OP link-with-neighbor.

The responding to the RFM may discard the received RFM when each nodereceives the RFM over the NOP link-with-neighbor. The responding to theRFM may comprise: when each node receives the RFM over an OPlink-with-neighbor, marking the link-to-neighbor as NOP if the RFM haseach node's own IP address among a list of non-reachable destinations;and invalidating the route using that link.

According to another aspect, a mobile device may comprise anon-transitory computer readable medium storing instructions to causethe mobile device to execute the method of any of claims 1-21.

According to another aspect, a mobile ad-hoc network comprise aplurality of nodes, each node communicating with the at least oneneighbor according to the routing method of any one of claims 1-21.

According to yet another aspect, there is provided a mobile ad-hocnetwork comprising: a plurality of point of attachment (PoA) forming acoverage area, each PoA configured to provide a communication link for amobile node; each PoA identifying a link quality metric for thecommunication link with the mobile node; the plurality of PoA locatedsuch that: when the mobile node is within the coverage area, the mobilenode has at least one operational link with at least one PoA of theplurality of PoA; when the mobile node moves within the area ofcoverage, the at least one operational link is degrading and thecommunication link with at least one other PoA is improving; and whenthe mobile node has only one operational link, a travel time for themobile node to travel between the PoA with the operational link to theat least one other PoA is less than a time for the mobile node to markthe operational link as non-operational and select the communicationlink as operational.

The link quality metric may be hysteresis-based.

Each PoA may compare the link quality metric received from anadvertisement with a high threshold and a low threshold. The linkquality metric may comprise: marking a link quality as high when thelink quality metric exceeds the high threshold: marking the link qualityas low when the link quality metric falls below the low threshold;marking the link quality as high when the link quality metric fallsbelow the high threshold, and before the link quality metric falls belowthe low threshold; marking the link quality as low when the link qualitymetric rises above the low threshold, and before the link quality metricexceeds the high threshold: and marking the link quality as low if atimeout timer for receiving the advertisement expires before receiving anew advertisement.

The link quality metric may be selected from at least one of: a receivedsignal strength indicator (RSSI), a Bit Error Rate (BER), a Signal toNoise Ratio (SNR), a Signal to Noise and Interference Ratio (SNIR), andany combination thereof. The low threshold may be selected to be higherthan a sensitivity of the mobile node.

The at least one operational link may be identified by: comparing ascore with a score-operational (SOP) criterion and with aScore-Non-Operational (SNOP) criterion. The at least one operationallink may be identified by: identifying a link-from-neighboroperationality and a link-to-neighbor operationality.

The link-from-neighbor operationality may comprise: marking thelink-from-neighbor as directionally Operational (OP) when the scoremeets the SOP criterion; marking the link-from-neighbor as directionallyNon-Operational (NOP) when the score meets the SNOP criterion; andkeeping the link-from-neighbor as a previous status when the score doesnot meet the SOP criterion and the SNOP criterion.

The link-to-neighbor operationality may comprise: marking thelink-to-neighbor as directionally NOP when each PoA does not find eachPoA's own IP address in the advertisement; marking the link-to-neighboras Going-Non-Operational (GNOP) when the score to the at least oneneighbor meets the SNOP criterion when each PoA finds each PoA's own IPaddress in the advertisement; and marking the link-to-neighbor asdirectionally OP when the score to the at least one neighbor does notmeet the SNOP criterion when each PoA finds each PoA's own IP address inthe advertisement.

The routing method may assure that link performance meets the broadbandrequirement during the transition time between the signal being lowerthan the break threshold and the actual decision of reconstructing theroute.

An aspect described herein may solve the unidirectional link problemthat arises due to nodes' movement and asymmetric transmission andreception conditions so as to promptly reconstruct broken routes. Theunidirectional link problem may be prevented to successfully reconstructbroken routes. Another aspect is accommodating sudden changes due tonode movement or any other factors in link status so that these suddenchanges may be detected quickly and broken routes may be promptlyreconstructed. An aspect described herein may have a rapid hand-offoccurring in three main conditions: (1) in normal conditions where thelink quality measure is changing gradually and in a bi-directionalmanner: (2) in a situation where the change is gradual but one directionbreaks much earlier than the other direction; and/or (3) when an abruptchange in signal quality such as occurs when for instance a vehicleturns into another street losing connection suddenly with a connectednode, and a new route to a new node has to be reconstructed.

The routing method may adapt to different QoS requirements and may havedifferent movement speeds. The routing method may assure the scalabilityof the seamless mobility solution by reducing the signal overhead neededfor route reconstruction and may adopt a distributed routereconstruction approach whereby any node in the network may make theroute reconstruction decision.

DESCRIPTION OF THE DRAWINGS

While the invention is claimed in the concluding portions hereof,example embodiments are provided in the accompanying detaileddescription which may be best understood in conjunction with theaccompanying diagrams:

FIG. 1 is a diagram showing a hysteresis-based handoff criterion betweentwo mobile devices;

FIG. 2 is a schematic diagram of an example of a mobile ad hoc network;

FIGS. 3(a)-3(b) illustrate a poorly and well-constructed MANET diagrams;

FIG. 4 is a flowchart illustrating a routine used for sendingadvertisement messages between the nodes;

FIG. 5 is a flowchart illustrating a link quality marking routine:

FIG. 6 is a diagram showing a hysteresis-based link quality markingcriterion;

FIG. 7 is a flowchart illustrating a link-from-neighbor operationalitydetermination process;

FIG. 8 is a flowchart illustrating a link-to-neighbor operationalitydetermination process;

FIG. 9 is a flowchart illustrating a routine used to respond to packettransmission failure to determine the link operationality of bothlink-from-neighbor and link-to-neighbor;

FIG. 10 is a flowchart illustrating a routine to determine whether thelink is bidirectionally operational;

FIGS. 11 (a)-11 (d) illustrate an example of a prior route constructionprocess;

FIG. 12 is a flowchart illustrating a routine used to respond toreceiving a Seek Route Message (SRM) in route construction;

FIG. 13 is a flowchart illustrating a routine used to respond toreceiving a Route Failure Message (RFM) in route construction;

FIG. 14 is a block diagram of a wireless communications-capable device;and;

FIG. 15 is an example of an advertisement message broadcasted by a node.

DETAILED DESCRIPTION

MANETs may comprise a fixed set of nodes acting as a network backhaulthrough which the mobile nodes travel. The fixed portion of the MANETmay be constructed in such a way that the network fulfills the followingconditions: (1) the mobile node has at least one Operational link at alltimes. The Operational link may be a link which meets a link qualitycriterion that ensures data can be transmitted and received by bothdevices forming that link. (2) Whenever the link quality between amobile node and a particular PoA is degrading, at least one link isimproving with another PoA. (3) In cases where the mobile node has onlyone operational link, the distance between fixed PoAs should ensurethat, at a speed of travel, a time for the mobile node to mark animproving link as operational is less than the time the mobile nodetakes to mark the degrading link as non-operational. As the network isnot infinite in scale, these three conditions may not be met at edges ofthe network, such as the mobile node is leaving the area of coverage, oralternatively the mobile node is entering the area of coverage. In thecases of the mobile node leaving a network coverage area or approachingthe coverage area, no handoff occurs.

FIG. 3 (a) shows an example of a poorly constructed network; whereas,FIG. 3 (b) shows an example of a well-constructed network. In FIG. 3(a), the mobile node A maintains connection to the network as long asthe mobile node A continues to travel in the B-D direction. The mobilenode A has two connections with B and D. The connection to PoA D isimproving and the connection to the PoA B is degrading. The mobile nodeA marks the connection to PoA D as operational before marking theconnection to PoA B as non-operational. Because of shadowing, the mobilenode A has not established connection with either PoA E or PoA C. Whenthe mobile node A makes a turn into the street in an E-C direction, themobile node A disconnects with both PoA B and PoA D (e.g. the linksbecome suddenly non-operational) before the mobile node A can establisha connection with PoA E or PoA C (e.g. the links become operational).Re-establishing a route may significantly disrupt any on-going datatraffic. In FIG. 3 (b), a PoA F has been placed at an intersectionoutside of the shadowing. This location enables the mobile node A tohave three connections (with PoAs B, D, and F). When the mobile node Amakes a turn, the connection with PoA F stays operational thusmaintaining the ongoing connection to the network. The third conditionas previously described ensures that the link with PoA C becomesoperational before the link with PoA F becomes non-operational. Thehandoff may be seamless and the data traffic may not be disrupted.

To support seamless mobility in MANET, only forwarding routeconstruction messages over bidirectional high-quality links are allowed.A hysteresis-based link quality marking mechanism may be used toidentify link quality. To identify link directionality, a modifiedneighbor advertisement mechanism may be used to identify linkdirectionality. To assure fast route reconstruction, an intelligentmechanism to filter route construction messages is used to assure fastroute reconstruction.

Three terms may be used to describe the link directionality.Link-from-neighbor, representing the direction from the neighbor to thelocal node. Link-to-neighbor, representing the direction from the localnode to the neighbor. Link-with-neighbor, representing the bidirectionallink between the local node and its neighbor.

Referring to FIG. 2, an example of a mobile ad hoc network 100 is shown.The network 100 includes a plurality of mobile nodes, such as A, and/orPoAs X, Y and Z collectively referred to as network nodes. The nodes maybe wireless routers, wireless Access Points (APs), laptop computers,tablets, mobile phones, and/or personal digital assistants (PDAs)connected by wireless communication links as appreciated by the skilledperson in the art. Each node communicates with one or more neighbors viathe wireless communication links.

Each node may periodically (e.g., every T_(A)) send one or moreadvertising messages, also referred to as advertisements, to the one ormore neighbors. Each advertising message may contain routeconstruction/break parameters as well as neighbors' link information,including their addresses and link qualities. FIG. 15 shows an exampleof an advertising message broadcasted by sender A (shown in FIG. 2).More specifically, a neighbor advertising message may comprise a numberof network parameters: a hysteresis low threshold (TL) and a highthreshold (TH) that may be used to identify a link quality; a number ofpacket retransmission tries (R) required before dropping a packet; anumber of dropped packets (N) required to mark a link asnon-operational; a timeout (T) before assuming that an advertisingmessage is lost; and/or an IP address as well as the last “j−1” linkquality marks for each neighbor that has an Operational (OP) link to thelocal node (OP link-from-neighbor). The list of neighbors and their linkqualities may keep changing whereas the rest of the parameters mayremain constant.

FIG. 14 depicts a block diagram of a mobile device 1400 executinginstructions to perform the handover. The Wireless Communications Unit1402 transmits and receives packets as well as determining a set ofphysical layer parameters (e.g., RSSI, BER, SNR, SNIR, etc.). Thewireless communications unit 1402 may provide a number of wirelesscommunication mediums, such as Bluetooth®, LTE, WiFi, and/or 5G. The CPU1404 executes instructions for determining a set of Medium AccessControl (MAC) layer parameters (e.g., number of transmissions retry,number of dropped packets, etc.) as well as executing the instructionsto determine the link quality and a link directionality. The memory unit1406 may store instructions and the node's local link parameters as wellas the neighbors' link info so the local link parameters can be invokedby the instructions responsible for marking the link quality and linkdirectionality.

The neighbor advertising messages may be used to identify the linkquality and the link directionality as well as assuring fast routereconstruction. The flowchart in FIG. 4 shows a routine 200 used forsending the neighbor advertisement messages. When a local node A, suchas a mobile phone, starts to communicate with one or more neighborsstarting at step 202, a neighbor list may first be extracted from adatabase (DB) by the local node A at step 204. Then the local node Apicks a selected neighbor, such as node X, from the one or moreneighbors at step 206. The link-from-X is detected if the selectedneighbor is operational (OP) at step 208 according to a hysteresis-basedlink quality marking mechanism as described herein. If the link isdetermined to be operational at step 208, then a last j−1 link-from-Xquality marks are extracted from a database at step 210. The node X info(e.g. IP address and the last j−1 link-from-X quality marks) is added tothe advertising messages at step 212. The node A keeps checking if thereare more neighbors at step 214. If the link-from-X is determined to benot operational at step 208, the node A keeps checking if there are moreneighbors at step 214. If a new neighbor exists, the new neighbor ispicked, and the process from step 208 to step 212 may be repeated to thenew neighbor. Otherwise, if there is no new neighbor, one or more routeconstruction/break parameters (e.g., TH_(A), TL_(A), R_(A), N_(A), andT_(A) where the subscript refers to the node itself) are added to theadvertising messages of the node A at step 216. Then the advertisingmessages are sent out at step 218. An advertisement timer is reset atstep 220. As the advertisement timer increases at step 222, the timer isread to determine if the timer exceeds a predetermined time limit T_(A)at step 224. If the timer does not exceed the time limit, the timerkeeps incrementing while the node A to send out more advertisementmessages. If the timer exceeds the time limit T_(A), the node A mayrestart the process from step 204 by extracting an updated neighbor listagain.

The neighbor advertising messages are used to identify the link qualityand the link directionality as well as assuring fast routereconstruction. To prevent a ping-pong effect, that is when a node keepshanding over forth and back between two adjacent PoAs due to signalfluctuations around a hand-over threshold, a hysteresis-based markingalgorithm is used to identify the link quality. For example, an RSSI ofthe neighbor advertising messages may be used based on thehysteresis-based marking algorithm to identify the link quality from theadvertising neighbor. The link quality mark may be later used todetermine the link operationality.

The hysteresis-based link quality marking mechanism is now discussed indetail with reference to FIG. 5. The flowchart illustrates a process 300used to mark the link quality based on the value of a Link QualityMeasurement (LQM) of the advertising messages as described herein. Thelink quality measurement may comprise the link RSSI, BER, SNIR, SNR,etc. and/or any combination thereof. Once the advertising messages arebroadcasted by a node, such as node X, the advertising messages may bereceived by the one or more neighbors at step 302. In particular, therecipient, such as node A, extracts the list of the neighbors and theircorresponding link quality marks at step 304 a. Meanwhile, advertisedroute construction/break parameters from the neighbor X, such asthreshold parameters THx and TLx, packet drop parameters Nx and Rx, andtimeout parameter T_(x) are extracted at step 304 b. The value of theLQM of the received advertising messages is determined at step 304 c andthe sender timeout timer is reset at step 304 d. As the processproceeds, the timeout timer keeps increasing at step 306. The advertisedroute construction/break parameters (e.g. TH_(x), TL_(X), T_(x), R_(X)and N_(X)) obtained at step 304 b may be compared with the local routeconstruction/break parameters (e.g. TH_(A), TL_(A), T_(A), R_(A) andN_(A)) to determine the link-with-X (e.g. those of link-from-X andlink-to-X) at step 308 (e.g. determine TH_(AX), TL_(AX), T_(Ax), R_(AX)and N_(AX)). More specifically, TH_(AX) and TL_(AX) are set to themaximum between the announced values and the local ones (e.g.TH_(AX)=max(TH_(A), TH_(X)), TL_(AX)=max(TH_(A), TH_(X))). T_(AX) is setto the advertised value plus a small time duration, ε (typical valuesfor a can be in few milliseconds), to account for transmission delays(e.g. T_(AX)=T_(X)+ε). R_(AX) and N_(AX) are set to a minimum betweenone or more announced values and one or more local ones (e.g.R_(AX)=min(R_(A), R_(X)), N_(AX)=min(TH_(A), TH_(X))). Theselink-specific parameters obtained at step 308 are stored in a databaseof the recipient at step 310, and are used as local parameters forevaluating next received advertisement messages. None of the minimumvalues should be advertised to keep the changes specific to each link.Unlike other solutions, the advertising route construction/breakparameters allows the network to locally adapt to different links' QoSrequirements without increasing a network-wide signaling overhead.

The value of the LQM of the last received advertising message determinedat step 304 c is then compared with the high threshold TH_(AX) and thelow threshold TL_(AX) based on the hysteresis mark algorithmdemonstrated according to the example shown in FIG. 6 to determine thelink quality. The details of how the link quality is marked are asfollows:

-   -   a. When the value of LQM of the received neighbor advertisement        determined at step 304 c exceeds the hysteresis high threshold        (TH_(AX)) at step 312, the link-from-X quality is marked as H at        step 314.    -   b. When the value of LQM of the received neighbor advertisement        determined at step 304 c falls below the hysteresis low        threshold (TL_(AX)), the link-from-X quality is marked as L at        step 318.    -   c. When the value of the LQM of the received neighbor        advertisement determined at step 304 c is below the hysteresis        TH_(AX) and above TL_(AX) at step 316, the last link-from-X        quality mark is determined at step 320. If the link quality was        marked as H in the last cycle, the link quality may also be        marked as H at this cycle at step 314. Otherwise, it may be        marked as L at step 318.    -   d. If the timeout timer for receiving an advertisement message        from a neighbor expires before the node receives an        advertisement from that neighbor at step 322, the        link-from-neighbor quality is marked as L at step 318. The        results of link quality are all saved in the local database of        the node.    -   e. Each time the advertisement message is successfully received,        the timeout timer is reset at step 304 d.

According to some aspects, the mobile nodes perform handoverinstructions when a link quality measurement falls below a sensitivitythreshold (Ts), below which the connection is considered broken. In thisinvention, TL is chosen to be significantly higher than Ts, as shown inFIG. 6, such that the link performance meets a specified broadbandrequirement during the transition time between the signal being lowerthan the hysteresis low threshold and the actual decision of marking thelink as non-operational. For example, if a minimum data rate isrequired, TL is set to a value that ensures the requirement is met. WhenRSSI is used as a link quality measure, typical values can be where Tsequals −92 dBm, then TL may be set to −80 dBm which would make sure thatthe link quality is maintained during the handover transitional period.

After the link-from-neighbor quality has been marked, the linkoperationality may be determined based on a score calculated by afunction of the last j link quality marks (j is a value that is selectedto maintain a balance between rapid response and stability), acquiredvia the neighbor advertisement technique previously described. Thisfunction may be either a statistical function (e.g., median, majorityvote, etc.) or a mathematical function, after assigning high and lowlink quality marks numerical values (e.g., numerical average, etc.). Forlink-from-neighbor, the j marks may be extracted from a databaserepresenting the last j link quality marks determined by process 300.For link-to-neighbor, the j marks are defined as follows: j−1 marksextracted from the DB (e.g. those extracted from the last neighboradvertisement in step 304 a) plus one always assumed as L.

FIG. 7 shows a flowchart to illustrate a routine 400 used to determine alink-from-neighbor operationality based on the neighbor advertisementmessages as described herein. Each time after the link-from-neighborquality, such as that for neighbor X, is marked at step 402, the last jmarks are extracted from a database at step 404. A score of link-from-Xis calculated at step 406. The link-from-X operationality is determinedas follows:

-   -   a. If the score meets the criterion for validating the link,        Score-Operational (SOP), at step 408:        -   The node marks the link-from-X as directionally Operational            (OP) at step 410.        -   The node starts advertising the IP address of that neighbor            as well as the last j−1 link-from-X quality marks (as stated            in routine 200 described above).            The SOP is consistent with the method used for calculating            the link-from-neighbor score in step 406 (e.g., if we use            the average value in step 406, the SOP would be a numerical            value representing when the link is validated.)    -   b. Otherwise, if the score meets the criterion for invalidating        the link, Score-Non-Operational (SNOP), at step 412:        -   The node marks the link-from-X as directionally            Non-Operational (NOP) at step 414.        -   The node stops advertising the neighbor IP address and the            link quality from that neighbor (as stated in routine 200            described above).            The SNOP is consistent with the method used for calculating            the link-from-neighbor score in step 406 (e.g., using the            average value in step 406, the SNOP would be a numerical            value representing when the link is invalidated.)    -   c. If the score does not meet the SOP and the score does not        meet the SNOP, the node maintains the previous mark. The last        link operationality is checked at step 416. If the link was OP,        the node marks the link-from-X also as OP. Otherwise, the node        marks the link-from-X as NOP.    -   d. All the results of the link-from-X operationality are saved        to a database of the node at step 418.

On the other hand, a link-to-neighbor operationality based on theneighbor advertisements as described herein is determined, andillustrated in the flowchart 500 in FIG. 8. Each time the advertisementis received. A list of the neighbors associated with the sender of theadvertisement is extracted at step 502. The node then checks if thenode's own IP address is in the neighbor list at step 504. The detailsof the link-to-neighbor operationality may be determined as follows:

-   -   a. When the node does not find its own IP address in the        neighbor advertisement at step 504, the node marks the link to        that neighbor as NOP at step 506.    -   b. When the node finds its own IP address in the neighbor        advertisement at step 504, the node extracts the last j−1        link-to-X quality marks at step 508. The node then calculates        the link score to that neighbor using the last j marks, using        the advertised last j−1 link quality marks and assuming that the        j^(th) mark is low (e.g. L), at step 510. The link-to-neighbor        score is compared with SNOP at step 512.        -   If the score does not meet the criterion for SNOP, the node            marks the link to that neighbor as Going-Non-Operational            (GNOP) at step 514.        -   Otherwise, the node marks the link to that neighbor as OP at            step 516.

All the results of the link operationality are saved in a database ofthe node at step 518.

In addition to the method described above to determine a linkoperationality based on received neighbor advertisements, the method mayrely on packet transmission failure to determine the link operationalityin both directions. Relying on packet transmission may be particularlyadept at detecting sudden drops in link quality caused by mobility dueto large-scale fading (e.g., turning around a corner). In cases where anode fails to transmit a packet to a neighbor, the process 600 todetermine the link operationality of both link-from-neighbor andlink-to-neighbor is shown in flowchart of FIG. 8, and is discussed asfollows:

-   -   a. When a node fails to transmit a packet to a neighbor at step        602, the packet retransmission counter, r, and packet drop        counter, n, are set to 0 at step 604.    -   b. The number of the packet retransmission counter is then        compared with a predetermined value of parameter R_(AX) at step        606. When the packet retransmissions counter for the neighbor        does not exceed R_(AX) at step 606, the node keeps        retransmitting the packet at step 608 and the transmission is        tested to see if the transmission fails again at step 610. If        failed, the number of packet retransmissions counter is        increased at step 612 and may be compared with the parameter        R_(AX) again to repeat the process.    -   c. When the packet retransmissions counter for a neighbor        exceeds R_(AX) at step 606, a dropped packet counter for that        neighbor is increased by 1 at step 614.    -   d. The number of the dropped packet counter is compared with a        predetermined value N_(AX) at step 616. When the dropped packet        counter for a neighbor does not exceed N_(AX) at step 616, the        packet retransmission counter is reset at step 618 and the        packet is retransmitted again at step 608.    -   e. When the dropped packet counter for a neighbor exceeds N_(AX)        at step 616,        -   The last j−1 link-from-neighbor marks are flushed,            preventing marking that link as OP for the next j marks at            step 620.        -   Both link-to-neighbor and link-from-neighbor are immediately            marked as NOP at step 622.        -   All the new link markings are then stored in a database at            step 624.    -   f. Each time a node succeeds in transmitting a packet to a        particular neighbor, the procedure ends at step 626 leaving the        link marks intact.

In addition to the situations discussed above, if and only if both linksfrom/to a neighbor are marked as OP, the link-with-neighbor is marked asbidirectionally OP. The flowchart in FIG. 9 depicts a process 700 todetermine whether the link is bidirectionally operational as follows.After link-to/from-neighbor operationality are marked at step 702, thelink-to-neighbor operationality is checked at step 704. If thelink-to-neighbor is marked OP at step 704, the link-from-neighbor isfurther checked at step 706.

-   -   a. If both link-from-neighbor and link-to-neighbor are marked        OP:        -   The node marks the link-with-neighbor as bidirectionally OP            at step 708.        -   The node starts forwarding packets over this link.    -   b. If either link-to-neighbor or link-from-neighbor is marked        NOP at step 704 and step 706, respectively:        -   The node marks the link-with-neighbor as bidirectionally NOP            at step 710.        -   The previous state of the link-with-neighbor is further            checked at step 712. If the previous link state was NOP,            then the node does nothing.        -   If the link-with-neighbor was marked as OP at step 712, the            node immediately invalidates all routes that use this link            at step 714.        -   Broadcasting a Route Failure Message (RFM) (e.g., RERR in            DSR and AoDV) is checked out whether it is required by the            routing method being used at step 716.        -   If the routing method being used does not require            broadcasting such a message at step 716, the node may still            broadcast the RFM at next step 718. RFMs may be sent to            upstream nodes (e.g. nodes closer to the route source),            using unicast transfer mode. Therefore, there is no            guarantee that the downstream node (e.g. the node with which            the connection has been lost) may receive this notification.            Broadcasting RFMs may be used, as will be explained in            routine 900, to help the downstream node in identifying when            bidirectional links become unidirectional.        -   The node then responds according to the routing method being            used at step 720.

As each node dynamically moves and/or experiences a degradation intransmission and/or reception, the link quality between the nodesperiodically changes. For example, as the distance between two mobilenodes increases, the link quality between the two mobile nodesdeteriorates. A route reconstruction may be used to update the link.However, due to the probabilistic differences in the transmission powerand receiver sensitivity, one node may likely mark the link asnon-operational before the other node (e.g., the link becomesunidirectional). When the node identifies that the link becamenon-operational, the other node may identify that link asnon-operational only after receiving the next neighbor advertisement.Hence, starting the route reconstruction process (e.g., sending the SeekRoute Message (SRM)) before sending the neighbor advertisement message(e.g., announcing the change in link directionality) may cause thereconstruction attempt to fail, significantly delaying the routereconstruction process.

FIG. 11 illustrates this problem in a detailed manner. Assume that nodeA communicates with node D via intermediate nodes B and C. When the linkbetween B and C becomes unidirectional due to node B movement away fromnode C, as shown in FIG. 11(a). When node B marks the link-form-C asNOP, node B responds by sending a Route Failure Message (RFM) (e.g., theRERR in DSR and AoDV) invalidating routes to destinations C and D, asshown in FIG. 11(b). When the node A receives that RFM, node A respondsby sending a Seek Route Message (SRM), such as the RREQ in DSR and AoDV,to reconstruct a route to D, as shown in FIG. 11(c). Since link-from-Bis not broken yet at node C, node A receives the SRM from B and discardsthe SRM from F. Then, node B rebroadcasts the SRM, as shown in FIG.11(c). When node D receives the SRM, node D responds by sending a RouteReturn Message (RRM), such as the RREP in DSR and AoDV. When node Creceives the RRM, node C sends the RRM to node B. However, the RRM maynot be transmitted successfully over a unidirectional link, causing theroute reconstruction process to fail. Only when node C receives theneighbor advertisement from node B, node C marks the link-with-B as NOP,discarding any received SRM from node B. After that the route from A toD can be reconstructed successfully through node F.

In order to solve the above problem, a route construction method usingintelligent filtering algorithm is described herein to reduce thereconstruction response time without increasing the signaling overhead.The intelligent route construction method includes a process to respondto receiving an SRM and a process to respond to receiving an RFM.Instead of reconstructing routes only when forwarding links' qualityseverely deteriorates, the solution described herein reconstructs routeswhen the forwarding links' quality falls below a predefined thresholdthat may be significantly above the link sensitivity threshold, therebymaintaining high QoS support. The intelligent route construction methodis discussed below in detail.

Referring to FIG. 12, the flowchart depicts a routine 800 used torespond to receiving an SRM. More specifically, when an SRM is receivedfrom a neighbor node, for example from node X, at step 802, the linkquality of link-with-neighbor is checked at step 804.

-   -   a. If the node receives an SRM over NOP link-with-neighbor at        step 804, the node discards the received SRM message at step        806.    -   b. If the node receives an SRM over an OP link-with-neighbor at        step 804:        -   If the link-to-neighbor is marked as GNOP at step 808, the            node discards the received SRM message. This operation may            prevent constructing routes over non-reliable links, as            receiving SRM from a neighbor could be triggered by the fact            that the link to that neighbor has become NOP.        -   Otherwise, the node responds to it at step 810 according to            the routing method being used.

On the other hand, a routine 900 used to respond to receiving an RFM isdepicted in the flowchart in FIG. 13. More specifically, when an RFM isreceived from a neighbor node, for example from node X, at step 902, thelink quality of link-with-neighbor is checked at step 904.

-   -   a. When the node receives an RFM over a NOP link-with-neighbor        at step 904, the node discards the received message at step 906.    -   b. When the node receives an RFM over an OP link-with-neighbor        at step 904:        -   If the RFM has the node's own IP address among the            non-reachable destinations (which can be determined via            routine 700 as an example) at step 908, the node immediately            marks the link-with-neighbor as NOP at step 910 (this            includes marking link-from/to-X as NOP) and invalidates the            route using that link.        -   Then, the node responds based on the routing method being            used at step 912.

As described herein may provide a scalable and fast routing method todetect changes in link status and to promptly reconstruct failed routesso as to enable seamless mobility within MANETs.

Unlike prior methods which require broadcasting extra control messages(e.g., signaling overhead), the methods described herein do not requiretransmitting any extra control message, facilitating fast routereconstruction without affecting the scalability of the solution orreducing the network capacity.

Instead of utilizing the reliable multicasting acknowledgementstechnique to detect sudden changes in link status, the methods describedherein rely on the normal unicast MAC-level acknowledgements to detectsudden changes, facilitating prompt route reconstruction withoutaffecting the scalability of the route reconstruction solution orreducing the network capacity.

Instead of reconstructing routes only when forwarding links' qualityseverely deteriorates, the methods described herein reconstructs routeswhen forwarding links' quality falls below a predefined threshold thatis significantly above the link sensitivity threshold, therebymaintaining high QoS support.

Instead of globally increasing the signaling overhead so as to reduceroute reconstruction response time, the methods described herein reducesthe response time only for mobile nodes, only increasing the signalingoverhead where and when the overhead is required to maintain stableconnections.

Instead of using both reactive and proactive solutions to reconstructroutes, the methods described herein use a proactive solution, reducingthe signaling overhead.

Instead of increasing the transmission rate of the advertisementmessages to reduce the reconstruction response time, the methodsdescribed herein intelligently respond to route construction messages,reducing the reconstruction response time without increasing thesignaling overhead.

The foregoing is considered as illustrative only of the principles ofthe invention. Further, since numerous changes and modifications willreadily occur to those skilled in the art, it is not desired to limitthe invention to the exact construction and operation shown anddescribed, and accordingly, all such suitable changes or modificationsin structure or operation which may be resorted to are intended to fallwithin the scope of the claimed invention.

What is claimed is:
 1. A routing method of a mobile ad-hoc network, themobile ad-hoc network including a plurality of nodes, each nodecommunicating with at least one neighbor via at least one communicationlink, the method comprising: each node transmitting an advertisement;each node identifying a link quality with each of the at least oneneighbor providing at least one mark based on a link quality metric;each node identifying a link operationality with each of the at leastone neighbor by evaluating a score calculated from the at least onemark; and each node reconstructing at least one route with the at leastone neighbor by filtering at least one route construction messagerelated to the link operationality of the at least one neighbor.
 2. Therouting method according to claim 1, wherein the link quality metric ishysteresis-based.
 3. The routing method according to claim 1, whereinthe step of identifying the link quality further comprises: comparingthe link quality metric received from the advertisement of the at leastone neighbor with a high threshold and a low threshold.
 4. The routingmethod according to claim 3, wherein the link quality metric comprises:marking the link quality as high when the link quality metric exceedsthe high threshold; marking the link quality as low when the linkquality metric falls below the low threshold; marking the link qualityas high when the link quality metric falls below the high threshold, andbefore the link quality metric falls below the low threshold; markingthe link quality as low when the link quality metric rises above the lowthreshold, and before the link quality metric exceeds the highthreshold; and marking the link quality as low if a timeout timer forreceiving the advertisement expires before receiving a new advertisementfrom the at least one neighbor.
 5. The routing method according to claim3, wherein the link quality metric is selected from at least one of: areceived signal strength indicator (RSSI), a Bit Error Rate (BER), aSignal to Noise Ratio (SNR), a Signal to Noise and Interference Ratio(SNIR), and any combination thereof.
 6. The routing method according toclaim 4, wherein the low threshold is selected to be higher than asensitivity of a recipient node.
 7. The routing method according toclaim 5, wherein the step of identifying link operationality furthercomprises: comparing the score with a score-operational (SOP) criterionand with a Score-Non-Operational (SNOP) criterion.
 8. The routing methodaccording to claim 7, wherein the step of identifying linkoperationality further comprises: identifying a link-from-neighboroperationality and a link-to-neighbor operationality.
 9. The routingmethod according to claim 8, wherein the step of identifying thelink-from-neighbor operationality comprises: marking thelink-from-neighbor as directionally Operational (OP) when the scoremeets the SOP criterion; marking the link-from-neighbor as directionallyNon-Operational (NOP) when the score meets the SNOP criterion; andkeeping the link-from-neighbor as a previous status when the score doesnot meet the SOP criterion and the SNOP criterion.
 10. The routingmethod according to claim 9, wherein the step of identifying thelink-to-neighbor operationality comprises: marking the link-to-neighboras directionally NOP when each node does not find each node's own IPaddress in the advertisement; marking the link-to-neighbor asGoing-Non-Operational (GNOP) when the score to the at least one neighbormeets the SNOP criterion when each node finds each node's own IP addressin the advertisement; and marking the link-to-neighbor as directionallyOP when the score to the at least one neighbor does not meet the SNOPcriterion when each node finds each node's own IP address in theadvertisement.
 11. The routing method according to claim 9, wherein thescore to the at least one neighbor is calculated based on the linkquality metric of an advertised last j marks.
 12. The routing methodaccording to claim 10, wherein the score to the at least one neighbor iscalculated based on the link quality metric of an advertised last j−1marks and assuming that the j^(th) mark has a low-quality.
 13. Therouting method according to claim 8, wherein a link-with-neighbor ismarked as bidirectionally OP when both link-from-neighbor andlink-to-neighbor meet the OP criterion.
 14. The routing method accordingto claim 8, further comprises: broadcasting a Route Failure Message(RFM) when a link-with-neighbor is marked as NOP.
 15. The routing methodaccording to claim 8, wherein the step of identifying linkoperationality further comprises: determining the link-from-neighboroperationality and the link-to-neighbor operationality under data packettransmission failure.
 16. The routing method according to claim 15,wherein the step of determining the link-from-neighbor operationalityand the link-to-neighbor operationality under data packet transmissionfailure further comprises: increasing a packet retransmission counter by1 when a data packet transmission has failed; increasing a droppedpacket counter by 1 when the data packet retransmission counter exceedsa predetermined number of retransmission tries, R; and marking both thelink-to-neighbor and the link-from-neighbor as NOP when the droppedpacket counter exceeds a predetermined number of dropped packets, N. 17.The routing method according to claim 16, further comprise:retransmitting data packet when the data packet retransmission counteris below the predetermined number of retransmission tries, R.
 18. Therouting method according to claim 16, further comprise: resetting thepacket retransmission counter, and retransmitting data packet when thedropped packet counter is below the predetermined number of droppedpackets, N.
 19. The routing method according to claim 14, wherein thestep of filtering route construction messages comprises responding to aSeek Route Message (SRM) from the at least one neighbor and respondingto the RFM from the at least one neighbor.
 20. The routing methodaccording to claim 19, wherein responding to SRM comprises: discardingthe received SRM when each node receives an SRM over a NOPlink-with-neighbor; and discarding the received SRM if thelink-to-neighbor is marked as GNOP when each node receives an SRM overan OP link-with-neighbor.
 21. The routing method according to claim 18,wherein responding to the RFM comprises: discarding the received RFMwhen each node receives the RFM over the NOP link-with-neighbor.
 22. Therouting method according to claim 19, wherein responding to the RFMcomprises: when each node receives the RFM over an OPlink-with-neighbor, marking the link-to-neighbor as NOP if the RFM haseach node's own IP address among a list of non-reachable destinations;and invalidating the route using that link.
 23. A mobile devicecomprising a non-transitory computer readable medium storinginstructions to cause the mobile device to execute the method ofclaim
 1. 24. A mobile ad-hoc network comprising a plurality of nodes,each node communicating with the at least one neighbor according to therouting method of claim
 1. 25. A mobile ad-hoc network comprising: aplurality of point of attachment (PoA) forming a coverage area, each PoAconfigured to provide a communication link for a mobile node; each PoAidentifying a link quality metric for the communication link with themobile node; the plurality of PoA located such that: when the mobilenode is within the coverage area, the mobile node has at least oneoperational link with at least one PoA of the plurality of PoA; when themobile node moves within the area of coverage, the at least oneoperational link is degrading and the communication link with at leastone other PoA is improving; and when the mobile node has only oneoperational link, a travel time for the mobile node to travel betweenthe PoA with the operational link to the at least one other PoA is lessthan a time for the mobile node to mark the operational link asnon-operational and select the communication link as operational. 26.The mobile ad-hoc network according to claim 25, wherein the linkquality metric is hysteresis-based.
 27. The mobile ad-hoc networkaccording to claim 25, each PoA compares the link quality metricreceived from an advertisement with a high threshold and a lowthreshold.
 28. The mobile ad-hoc network according to claim 27, whereinthe link quality metric comprises: marking a link quality as high whenthe link quality metric exceeds the high threshold; marking the linkquality as low when the link quality metric falls below the lowthreshold; marking the link quality as high when the link quality metricfalls below the high threshold, and before the link quality metric fallsbelow the low threshold; marking the link quality as low when the linkquality metric rises above the low threshold, and before the linkquality metric exceeds the high threshold; and marking the link qualityas low if a timeout timer for receiving the advertisement expires beforereceiving a new advertisement.
 29. The mobile ad-hoc network accordingto claim 25, wherein the link quality metric is selected from at leastone of: a received signal strength indicator (RSSI), a Bit Error Rate(BER), a Signal to Noise Ratio (SNR), a Signal to Noise and InterferenceRatio (SNIR), and any combination thereof.
 30. The mobile ad-hoc networkaccording to claim 27, wherein the low threshold is selected to behigher than a sensitivity of the mobile node.
 31. The mobile ad-hocnetwork according to claim 27, wherein the at least one operational linkis identified by: comparing a score with a score-operational (SOP)criterion and with a Score-Non-Operational (SNOP) criterion.
 32. Themobile ad-hoc network according to claim 31, wherein the at least oneoperational link is identified by: identifying a link-from-neighboroperationality and a link-to-neighbor operationality.
 33. The mobilead-hoc network according to claim 32, wherein the link-from-neighboroperationality comprises: marking the link-from-neighbor asdirectionally Operational (OP) when the score meets the SOP criterion;marking the link-from-neighbor as directionally Non-Operational (NOP)when the score meets the SNOP criterion; and keeping thelink-from-neighbor as a previous status when the score does not meet theSOP criterion and the SNOP criterion.
 34. The mobile ad-hoc networkaccording to claim 33, wherein the link-to-neighbor operationalitycomprises: marking the link-to-neighbor as directionally NOP when eachPoA does not find each PoA's own IP address in the advertisement;marking the link-to-neighbor as Going-Non-Operational (GNOP) when thescore to the at least one neighbor meets the SNOP criterion when eachPoA finds each PoA's own IP address in the advertisement; and markingthe link-to-neighbor as directionally OP when the score to the at leastone neighbor does not meet the SNOP criterion when each PoA finds eachPoA's own IP address in the advertisement.